Balance with gas-tight housing



1965 H. G. WIEDEMANN 3,194,332

BALANCE WITH GAS-TIGHT HOUSING Filed Dec. 7, 1964 2 Sheets-Sheet lTNVENTOR HANS GEORG WIEDEMANN MXM ATTORNEY y 1965 H. G. WIEDEMANN3,194,332

BALANCE WITH GAS-TIGHT HOUSING Filed Dec. 7, 1964 2 Sheets-Sheet 2 HANSGEORG wlgf/a r lsl BY M ATTORNEY United States Patent 3,194,332 BALANCEWITH GAS-THGHT HOUSING Hans Georg Wiedeinann, Stafa, Switzerland,assignor to Mepag, A.G., Zurich, Switzerland, a corporation ofSwitzerland Filed Dec. 7, 1964, Ser. No. 416,557 Claims priority,application Switzerland, Feb. 19, 1964, Lass/e4 Claims. (Cl. 177-241)This invention relates to a balance, and more particularly to a balancehaving a gas-tight housing. The gastight housing encloses at least thebeam of the balance and, suspended from one arm of the balance beam, thehanger attachment provided with the specimen bowl. In order to weigh thespecimen under experimental conditions which dir'ler considerably fromthe working conditions under which the various parts of the balanceenclosed by the gas-tight housing can operate reliably, an elongatedbell is usually provided on the gas-tight housing into which thespecimen bowl and the adjacent part of the hanger attachment project. Inorder to Weigh the specimen at temperatures differing greatly from thenormal room temperature, that end of the bell which is directed awayfrom the balance housing and which encloses the specimen bowl isimmersed a correspondingly dimensioned cooling or heating means.

This type of the balance, with a gas-tight housing, having a bell-shapedmember attached thereon, is frequently referred to as a thermo-balance.Such balances have various deficiencies, as experience has shown, whichrender a wider practical application diiiicult. This is particularlytrue if the specimen to be weighed gives on corrosive gases. Even ifthese gases are pumped out of the balance housing continuously, it isinevitable that a. part of the gases will come in contact with the knifeedges of the balance beam and, in time, will cause the destructionthereof. Even more unfavourable in this respect are experimentalconditions in which the specimens are weighed in a corrosive gaseousatmosphere having a high temperature. But even when a non-corrosivegaseous atmosphere is used, the hitherto conventional thermo-balancesstill exhibit deficiencies if the sample has to be weighed in a flow ofgas which, in the region of the bell, is subjected to considerablydifferent temperatures than prevail inside the housing of the balance.Due to the flow of gas, heat conveyance occurs which is a function ofthe velocity of the gas flow, and the said heat makes it virtuallyimpossible to maintain an adequately constant temperature inside thehousing of the balance.

The present invention aims to provide a thermobalance which does notexhibit the drawbacks briefly mentioned above. Accordingly, thisinvention relates to a balance comprising a gas-tight housing, a balancebeam fulcrumed inside said housing, a bell-shaped member detachablyconnected to said gas-tight housing, a tube protruding into saidbell-shaped member and providing communication between the interior ofsaid bell-shaped member and the interior of said gas-tight housing, agas outlet leading out from the annular space formed by said tube andsaid bell-shaped member, a hanger attachment pivoted on one arm of saidbalance beam and protruding through said tube into said bell-shapedmember, and a specimen bowl located inside said bell-shaped member andfastened to one end of said hanger attachment. A still further object ofthe invention is to provide, in a thermo-balance of the kind outlined,an annular flange detachably inserted between said gas-tight housing andsaid bell-shaped member, which flange carries said tube and includessaid gas outlet and a gas inlet discharging into said tube.

These and other modifications and the advantages of the invention willbest be understood from the following description of a specificembodiment when read in connection with the accompanying drawing inwhich:

FIG. 1 is a cross-section through the balance housing with thebell-shaped member in place, and

FIG. 2 is a cross-section through the protective battle shown in P16. 1,on a much larger scale than that of FIG. 1. i

The gas-tight balance housing is formed by a cylindrical double jacket 3and side walls 4 which may be detachably fastened to the jacket 3. Inorder to evacuate the housing, there is provided a gas outlet 6,closable by a valve or gate 5, for connection with a suction pump 7. Agas inlet 9, closable by a valve or gate 8, is also provided to fill thehousing with a gas of suitable composiiton when required. Inside thehollow space 10 bounded by the parts 3 and 4 of the housing, the balancebeam 12 is fulcrurned on a support member 11 inside the housing of thebalance. On the shorter arm of the beam 12,

provided with a terminal knife-edge, is pivoted a hanger attachment.This hanger attachment has a stirrup member 13 and in the regionvertically above and below the member 13 the balance housing has twoconnecting flanges 14 and 15 each of which incorporates an aperture 16,17, respectively, both of which are in communication with the hollowspace 10. Apart from the stirrup member 13 the hanger attachmentcomprises, if required, additional weights 13 and, further, a rod 19projecting upwardly through the aperture 16 or downwardly through theaperture 17. In FIG. 1 a rod 19 protruding upwardly through the aperture16 is shown. On the end of the rod 19 which is directed away from thestirrup member 13, a specimen bowl 20 is fastened. The rod 19 and thebowl 20 generally consist of a ceramic material which is suiiicientlyresistant to the gases likely to be encountered. A bell-shaped member21, which generally consists of glass or ceramic, into the inside 22 ofwhich the specimen bowl 2% protrudes, is now detachably fixed to anannular flange 23 which in turn is connectable to the upper connectionflange 14 or to the lower connection flange 15 of the balance housing.The flange of the balance housing which is not used to fasten thebell-shaped member 21 is provided with a cover 24 as shown in FIG. 1where said cover 24 is fitted to the lower connection flange 15. Amulti-section bathe 25 is secured in the bore of the annular flange 23at the end which is near the housing, the preferred embodiment of saidbaffle 25 being shown in FIG. 2. The rod 19 of the hanger attachmentpasses with adequate lateral play freely through this battle 25. Theouter jacket 26 of the aide, made from thin metal plate, is bent backinwardly .at one end to form an annular groove 27. A number of screenplates 28, in the form of shallow truncated cones, are coaxially mountedinside of the outer jacket 26. At least the screen plate nearest thegroove 27 overhangs, at a distance therefrom, the returned inner edge ofthe outer jacket 26. The screen plates 28 are attached to the outerjacket 26 by means of one or more thin webs 29.

According to FIG. 1, the annular flange 23 furthermore has a gas inlet39, which is provided with a valve or gate 31 and which discharges intothe bore of the an nular flange 23, said here widening outwardly fromthe baflie 25. Looking in the direction towards the bellshaped member21, the bore in the annular flange 23 is again widened until itsdiameter is virtually the same as the inside diameter of the bell-shapedmmeber 21. This widest portion of the bore is penetrated by a tube 32 ofsubstantially smaller diameter, so that an annular space 33 is formedwhich is in communication with an annular space 34 bounded by the tube32 and the bell-shaped member 21. The base portion of the tube 32 isattached to the annular flange 23 at the base of the widest portion or"its bore. The tube protrudes into the bellshaped member 21 sufiicientlyto discharge adjacent the specimen bowl 249. The rod 19 carrying thespecimen bowl 2% passes through the tube 32. A gas outlet 35 is providedapproximately halfway along the annular space 33 in the annular flange23, and a cooling trap 37 is usually fitted to the connecting flange 36of the gas outlet 35. The cooling trap 37 can in turn be provided with agas outlet 39 closable by a valve or gate 38 and, if necessary, can beconnected, through a further valve or gate as, to a suction pump 41.Finally, in order to be able to use the balance to weigh a specimenmarkedly difierent in temperature from normal room temperature, acooling or heating means 42 is placed over that portion of thebell-shaped member 21 which encloses the specimen bowl 20, the heatingor cooling means being only shown diagrammatically in FIG. 1. Furthercomponents of the balance, such as the supports or consoles for thehousing and for the suction pumps 7 and 41 are not shown in FIG. 1 forreasons of clarity.

The most discriminating demands on the balance described arises if, forexample, the specimen is to be weighed in a flow of corrosive gas athigh temperature. For this purpose, the preferable procedure is asfollows. With the heating means 42 and the bell-shaped member 21removed, the specimen to be weighed is placed in the bowl 20. The baffle25 prevents any portions of the specimen which are split by negligencefrom penetrating the inner space 10 of the balance housing. After thebell-shaped member 21 has been mounted on the annular flange 23 and theheating means 42 fitted over the bellshaped member 21, both pumps 7 and41 are set in motion with the valves or gates 8, 31, 38 closed and withthe valves or gates 5 and 40 open, in order to evacuate the housing ofthe balance and also the bell-shaped member 21. The heating means 42 maynow be operated so that the bowl 20 and the specimen contained therein,are brought to the desired temperature. When this has been done, thevalve or gate 5 may be closed, the pump 7 switched oft" and, by a slightopening of the valve or gate 3, a noble or other inert gas can be let inthrough the gas inlet 9. This protective gas flows through the housingof the balance, then through the aperture 16 and the bafile 25, and (viathe tube 32, it reaches the interior of the bell-shaped member 21. Fromthence it is sucked through the annular spaces 34- and 33 to the gasoutlet 35, to be cooled by the trap 37 and sucked away by means of thepump 41. The corrosive gas which is to flush around the specimen is fedthrough the valve or gate 31 to the gas inlet 30. From there, togetherwith the protective gas, it flows through the tube 32 into the hollowspace 22 of the bell-shaped member 21. Extraction occurs in the manneralready explained, through the annular spaces 34 and 33, through the gasoutlet 35 and cooling device 37, by means of the pump 41. Byappropriately regulating the two valves or gates 8 and 31, it ispossible to maintain a gas pressure inside the balance housing, which isslightly higher than the gas pressure inside the tube 32 and thebell-shaped member 21, thus preventing the corrosive gas from enteringthe balance housing, so that the vital parts of the balance areeffectively safeguarded against any attack by corrosive gases. This canalso be achieved in a corresponding manner it high gas pressures are tobe maintained inside the balance housing and the bell-shaped member 21.In this case,

the valve or gate 40 is closed, the pump 41 stopped and the valve orgates 8, 31 and 38 accordingly opened and regulated.

If the temperautre inside the bell-shaped member 21 is much higher thaninside the balance housing the baille 25 will reflect a considerablepart of the radiated heat and so safeguard the hanger attachment and theshorter arm of the balance beam 12 against excessive heating.Furthermore, along the tube 32, there will be a considerable temperaturedrop which may lead to the formation of condensate on the colder partsof the tube. The condensate formed on the outside of the tube 32 canonly drip into the annular space 33, in which it is collected. Thecondensate formed on the inside of the tube 32 will, however, collect inthe annular space bounded by the cylindrical jacket of the baflie 25 andthe inside of the bore in the annular flange 23. If condensate shouldform on the inside of the jacket 26 or on the screen plates 28 of thebaffle 25 (FIG. 2), the same will be trapped in the groove 27. In thisWay, even during prolonged use of the balance, condensate which isfrequently highly active chemically is prevented from penetrating thebalance housing, and from destruction of balance components therein. Byvirtue of the detachable connection of the annular flange 23 on thebalance housing all components which are subject to dirt or wear canreadily be removed, and, if necessary, cleaned or replaced, whilst thebalance parts inside the balance housing are protected and only requirenormal maintenance.

I claim:

1. A balance with a gas-tight housing comprising a balance beamfulcrumed inside said housing, a bell-shaped member detachably connectedto said housing, a tube protruding into said bell-shaped member andproviding a communication between the interior of said gas-tight housingand the interior of said bell-shaped member, a gas outlet leading outfrom the annular space formed by said tube and said bell-shaped member,a hanger attachment pivoted on one arm of said balance beam andprotruding through said tube into said bell-shaped member, and aspecimen bowl located inside said bell-shaped member but outside saidtube and fastened to a protruding part of said hanger attachment.

2. The invention as recited in claim 1, wherein a first gas inlet isprovided which discharges into said gas-tight housing and wherein asecond gas inlet is provided which discharges into said tube.

3. The invention as recited in claim 2, wherein a multisection baflle isinserted between said second gas inlet and the interior of saidgas-tight housing, which bafile encloses the projecting part of saidhanger attachment with lateral clearance.

4. A balance with a gas-tight housing comprising a balance beamfulcrumed inside said gas-tight housing, an annular flange detachablyfastened to said gas-tight housing, the bore of said annular flangecommunicating with the interior of said gas-tight housing, a bell-shapedmember detachably connected to said annular flange, a tube mounted onsaid annular flange, said tube protruding into said bell-shaped memberand providing a communication between the bore of said annular flangeand the interior of said bell-shaped member, a gas outlet leading outfrom the annular space formed by the outside of said tube and the insideof said annular flange, said annular space being in communication withthe annular space formed by the protruding part of said tube and saidbell-shaped member, a hanger attachment pivoted on one arm of saidbalance beam, said hanger attachment having a rod protruding throughsaid annular flange and said tube into said bell-shaped member, and aspecimen bowl fastened to said rod in the region inside said bell-shapedmember but outside said tube.

5. The invention as recited in claim 4, wherein said flange has a gasinlet discharging into its bore and where in in the region between saidgas inlet and the interior of said gas-tight housing a multi-sectionbaflie is inserted 5 6 in said bore of the flange, which bafiie enclosessaid rod FOREIGN PATENTS W101 lateral play- 29,236 12/13 Great Britain.References Cited by the Examiner 77, 9/ 1 at ita n- 877,429 1/ 62 GreatBritain UNITED STATES PATENTS 5 3,027,985 4/62 Gavloffsky 177-480 X LEOSMILOW, Primary Examiner. 3,061,027 10/62 Berge et a1 177-210 X

1. A BALANCE WITH A GAS-TIGHT HOUSING COMPRISING A BALANCE BEAMFULCRUMED INSIDE SAID HOUSING, A BELL-SHAPED MEMBER DETACHABLY CONNECTEDTO SAID HOUSING, A TUBE PROTRUDING INTO SAID BELL-SHAPED MEMBER ANDPROVIDING A COMMUNICATION BETWEEN THE INTERIOR OF SAID GAS-TIGHT HOUSINGAND THE INTERIOR OF SAID BELL-SHAPED MEMBER, A GAS OUTLET LEADING OUTFROM THE ANNULAR SPACE FORMED BY